The present invention is directed to processes for extracting contaminants from soil liquids and gases along paths of preferential flow in the ground. More specifically, the present invention is directed to processes for selectively extracting contaminants by high-vacuum techniques from at least two different preferential flow paths in the ground with a single well. One embodiment of the present invention is directed to a process for removing contaminants from a contaminated area of the ground comprising soil having a first permeability, said ground having a plurality of paths of preferential flow, each path having a permeability at least ten times greater than the first permeability, which process comprises providing a borehole in the contaminated area to intersect at least a first path of preferential flow and a second path of preferential flow, said second path of preferential flow being situated at a depth greater than said first path of preferential flow; placing in the borehole a first vacuum extraction pipe having a bottom opening situated within the first path of preferential flow and a second vacuum extraction pipe having a bottom opening situated within the second path of preferential flow; isolating the first path of preferential flow from the second path of preferential flow so that a vacuum applied to the first vacuum extraction pipe with a bottom opening situated in the first path of preferential flow will extract gases and liquids from the first path of preferential flow but not from the second path of preferential flow and a vacuum applied to the second vacuum extraction pipe with a bottom opening situated in the second path of preferential flow will extract gases and liquids from the second path of preferential flow but not from the first path of preferential flow; applying a vacuum to at least one of the vacuum extraction pipes to draw gases and liquid from at least one of the paths of preferential flow into a vacuum extraction pipe and transport both the gases and the liquid to the surface as a common stream; forming from the common stream a stream which is primarily liquid and a stream which is primarily gaseous; and removing contaminants from at least one of the liquid stream and the gaseous stream. Another embodiment of the present invention is directed to an apparatus for removing contaminants from a contaminated area of the ground comprising soil having a first permeability, said ground having a plurality of paths of preferential flow, each path having a permeability at least ten times greater than the first permeability, said contaminated area of the ground being provided with a borehole extending downwardly from the surface of the ground to intersect at least a first path of preferential flow and a second path of preferential flow, said second path of preferential flow being situated at a depth greater than said first path of preferential flow, said apparatus comprising at least a first vacuum extraction pipe and a second vacuum extraction pipe situated inside of the borehole, wherein the first vacuum extraction pipe has a bottom opening situated within the first path of preferential flow and the second vacuum extraction pipe has a bottom opening situated within the second path of preferential flow, said first path of preferential flow being isolated from said second path of preferential flow so that a vacuum applied to the first vacuum extraction pipe with a bottom opening situated in the first path of preferential flow will extract gases and liquids from the first path of preferential flow but not from the second path of preferential flow and a vacuum applied to the second vacuum extraction pipe with a bottom opening situated in the second path of preferential flow will extract gases and liquids from the second path of preferential flow but not from the first path of preferential flow; a vacuum-forming apparatus in fluid communication with the first vacuum extraction pipe and the second vacuum extraction pipe and adapted to form a zone of reduced pressure in the first and second paths of preferential flow around the borehole, whereby gases and liquid can be drawn from the first and second paths of preferential flow into a vacuum extraction pipe and conveyed to the surface as a common stream; a vapor-liquid separator in fluid communication with said vacuum-forming apparatus and said first and second vacuum extraction pipes, wherein said vapor-liquid separator separates the common stream into separate gas and liquid streams; and a contaminant removal system, said contaminant removal system being situated to remove contaminants from at least one of the liquid stream and the gas stream.
Contaminants can exist in subsurface soil and groundwater in the liquid or vapor phase as discrete substances and mixed with and/or dissolved in groundwater and soil gases. Various contaminants can be found in groundwater and soil, such as volatile compounds, including volatile organic compounds, nonvolatile materials, metal contaminants, and the like. Such contaminants can be found and dealt with in the vadose (unsaturated) zone found between the surface of the earth and the water table, at the interface between the vadose zone and the water table, and in the saturated zone below the water table.
At many industrial and commercial facilities and at waste handling and disposal sites, soil and groundwater are contaminated With suspended or water-soluble chemicals, or both. A variety of techniques have been used for removal of contaminants and remediation of affected soil. One common technique entails the excavation and off-site treatment of the soil. Another technique entails saturating the contaminated soil with water in situ, causing the contaminants to be leached slowly from the soil by the water. The contaminated water can then be removed.
Techniques have also been proposed for removing volatile organic contaminants from soil by vacuum extraction. For example, in U.S. Pat. No. 4,323,122, it was proposed that a vacuum be applied in a borehole at the level of the water table, the assumption being that a contaminant such as gasoline, which is lighter than water, would float on the water table and present a layer that could be drawn off by vacuum applied to the liquid at or around that level. U.S. Pat. No. 4,323,122 (Knopik) discloses a system and method for recovering organic liquid such as gasoline which has settled on the water table in underground areas. The system comprises a conduit extending from the ground surface to a point just above the water table, a collection head fitted on the lower end of the conduit, a collection vessel connected to the upper end of the conduit, and an exhaust means for creating less than atmospheric pressure in the vessel. The collection head has a liquid impermeable end portion and a liquid permeable intermediate portion for permitting the passage of liquid. The process comprises providing an opening in the ground to a point beneath the surface of the water table, positioning the conduit with the collection head in place so that the liquid permeable wall of the collection head is just above the surface of the water table, connecting the conduit to the collection vessel intake, and exhausting air and other gaseous materials from the vessel to cause liquid to flow into the collection head through the conduit into the vessel.
Others have suggested the possibility of venting soil above the water table (i.e., in the vadose zone) to cause vaporization of the contaminant in the soil, and then drawing off the contaminant in the vapor phase. Groundwater requiring treatment is in such processes conventionally removed by pumping from separate conventional water wells. In situations in which water does flow into vacuum extraction wells, it has been suggested that a second, liquid phase pump be placed either in the well or at the surface to remove the water through a second conduit. For example, U.S. Pat. No. 4,660,639 (Visser et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for the removal of volatile contaminants from the vadose zone of contaminated ground by extracting volatilized contaminants from the vadose zone by way of one or more vacuum extraction wells. The process entails drilling one or more wells into the subsurface media in the contaminated area, the well being constructed so that fluids in the vadose zone can flow into the well, whereas the liquid in the saturated zone below the water table cannot substantially flow into the well. The borehole and conduit of the well can optionally extend below the water table, in which case the vacuum applied to the upper portion of the conduit will be effective to draw contaminant from the vadose zone, but insufficient to draw a significant amount of water from the saturated zone into the conduit. If it is desired to remove groundwater from below the water table, this removal is accomplished either by a separate sampling device situated in the borehole or through a separate well.
In addition, Stinson, "EPA Site Demonstration of the Terra Vac In Situ Vacuum Extraction Process in Groveland, Mass.", Air & Waste Management Association, Vol. 39, No. 8, pages 1054 to 1062 (1989), the disclosure of which is totally incorporated herein by reference, discloses an evaluation of an in situ vacuum extraction process. The process entails removal of contaminants from the vadose zone by vacuum. Wells are installed in the contaminated vadose soil. A vacuum pump or blower induces air flow through the soil, stripping and volatilizing volatile organic compounds from the soil matrix into the air stream. Liquid water, if present in the soil, is also extracted along with the contamination. The two-phase stream of contaminated air and water flows to a vapor/liquid separator where contaminated water is removed. The contaminated air stream then flows through a treatment system such as gas-phase activated carbon to remove contaminants from the air stream. The clean air is exhausted to the atmosphere through a vent. U.S. Pat. No. 4,593,760 (Visser et al.), the disclosure of which is totally incorporated herein by reference, and U.S. Pat. No. Re. 33,102, the disclosure of which is totally incorporated herein by reference, also disclose processes for removal of volatile contaminants from the vadose zone of contaminated ground by pumping Volatilized contaminants from the vadose zone using one or more vacuum extraction wells.
"Forced Venting to Remove Gasoline Vapor from a Large-Scale Model Aquifer," American Petroleum Institute, Health and Environmental Sciences Department, API Publication No. 4431 (1984) discloses the results of experiments examining forced venting of air through the soil above a gasoline spill in a model aquifer. Various flow rates and geometries for the venting plumbing were used to determine the most efficient method of removing gasoline from the underground environment and lowering gasoline vapor concentrations in the unsaturated zone above the spill.
"Venting for the Removal of Hydrocarbon Vapors from Gasoline Contaminated Soil," J. Thornton and W. Wootan, J. Environ. Sci. Health, A17(1), 31-44 (1982) discloses the results of an experiment investigating the use of a venting strategy to remove gasoline vapors from contaminated soil strata. A contained gasoline leak was created in a large outdoor facility which simulates soil strata and a static water table. An air flow was established, and vapor samples taken before, during, and after venting were checked for hydrocarbon content.
U.S. Pat. No. 2,605,637 (Rhoades), the disclosure of which is totally incorporated herein by reference, discloses a method of subterranean surveying to determine the liquid levels of a plurality of superimposed fluid bearing strata through a single drill hole. A plurality of tubes are housed within a single drill hole. The tubes are positioned at varying subterranean fluid bearing strata and are used to measure liquid levels in each of the isolated strata.
U.S. Pat. No. 2,925,097 (Duesterberg), the disclosure of which is totally incorporated herein by reference, discloses a tubular member adapted to be positioned in the flow string of an oil or gas well. A plurality of flow tubes are placed within a wellbore for removing well fluids. The tubes comprise a perforate section that prevents cutting out or eroding caused by high fluid pressure or abrasive fluids.
U.S. Pat. No. 4,834,178 (Knecht et al.), the disclosure of which is totally incorporated herein by reference, discloses a process and apparatus for fireflooding with liquid heat transfer media comprising injection of oxidant gas and liquid heat transfer media into a well through separate conduits, the liquid conduit downstream end submerged in a liquid volume, so as to form a seal and prevent oxidant gas migration into the liquid conduit.
U.S. Pat. No. 5,161,613 (Jones), the disclosure of which is totally incorporated herein by reference, discloses a method and apparatus for treating multiple strata in a single operation from a single wellbore which penetrates a treatment interval which, in turn, includes a plurality of strata which, in turn, have different permeabilities. A treating fluid, such as a consolidating agent, acid, or the like, is delivered directly to different levels within a section of the wellbore adjacent the interval to be treated through a plurality of alternate paths which, in turn, lie substantially adjacent to the strata to be treated.
U.S. Pat. No. 5,190,108 (Mansuy), the disclosure of which is totally incorporated herein by reference, discloses the inhibition of biological fouling of water wells by replacing the air in the well column with an anoxic gas such as nitrogen to deprive aerobic bacteria of oxygen. The anoxic gas is applied from a cylindrical tank at the surface and through a gas pipe extending from the tank down into the well casing. The well casing is sealed near the top to prevent air infiltration and maintain a positive gas pressure. The anoxic gas is applied at a slightly positive pressure to maintain the well column filled with it and to prevent air penetration. The gas can be supplied to the well column only or to both the well column and the aquifer so that a blanket of gas in the area of the well inhibits air penetration of the water from the unsaturated cover layer above the aquifer.
U.S. Pat. No. 5,246,070 (Greve et al.), the disclosure of which is totally incorporated herein by reference, discloses a method for completing a groundwater monitoring site including several monitoring points disposed at different depths. The piping includes a single multi-conduit pipe having a smooth, tightly packable outer wall and being composed of individual pipe lengths which are coupled to each other in a sealed relationship. The pipe lengths are subdivided in the longitudinal direction into several conduits by partition walls and are coupled to each other in such a fashion that their conduits are in relative alignment at the junctures and not reduced in area. For the purpose of providing filter sections for the admission of water, individual pipe lengths are provided in their outer wall with filter slots in the area of one or several conduits.
U.S. Pat. No. 5,050,676 (Hess et al.) and U.S. Pat. No. 5,197,541 (Hess et al.), the disclosures of each of which are totally incorporated herein by reference, disclose apparatus and processes for two phase vacuum extraction of contaminants from the ground which entails vacuum withdrawal of liquid and gaseous phases as a common stream, separation of the liquid and gaseous phases, and subsequent treatment of the separated liquid and gases to produce clean effluents. Two phase vacuum extraction employs a single vacuum generating device to remove contaminants in both the liquid stream and soil gases through a single well casing.
U.S. Pat. No. 5,172,764 (Hajali et al.), the disclosure of which is totally incorporated herein by reference, discloses an apparatus and process for removing contaminants from a contaminated area of the ground having a vadose zone and a water table which comprises providing a borehole in the contaminated area; placing in the borehole a perforated riser pipe inside of which is situated a vacuum extraction pipe with an opening situated near, at, or at any point below the water table within the perforated riser pipe; while introducing a gas into the riser pipe, applying a vacuum to the vacuum extraction pipe to draw gases and liquid from the soil into the perforated riser pipe and from the riser pipe into the vacuum extraction pipe and transport both the gases and the liquid to the surface as a common stream; forming from the common stream a stream which is primarily liquid and a stream which is primarily gaseous; and separately treating the separated liquid and gas streams.
U.S. Pat. No. 5,076,360 (Morrow), the disclosure of which is totally. incorporated herein by reference, discloses methods and apparatus for vacuum extraction of contaminants from the ground which, in a preferred embodiment, entails vacuum withdrawal of liquid and gaseous phases as a common stream, separation of the liquid and gaseous phases, and subsequent treatment of the separated liquid and gases to produce clean effluent. A primed vacuum extraction employs a single vacuum generating device to remove contaminants in both the liquid stream and soil gases through a single well casing utilizing a priming tube which introduces air or other gas to the liquid collected at the bottom of a well. The method permits vacuum extraction of both liquids and gases from the subsurface by way of wells having a liquid layer which is more than thirty feet below the soil surface or in which a screened interval of the extraction pipe is entirely below the liquid surface.
U.S. Pat. No. 5,358,357 (Mancini et al.), entitled "Improved Process and Apparatus for High Vacuum Groundwater Extraction," the disclosure of which is totally incorporated herein by reference, discloses a process and apparatus in which vacuum extraction is used to remove soil contaminants in both the saturated and vadose zones. One embodiment of the invention is directed to a process for removing contaminants from a contaminated area of the ground having a vadose zone and a water table, which comprises providing a borehole in the contaminated area to a depth below the water table; placing in the borehole to a depth below the water table a perforated riser pipe inside of which is situated a vacuum extraction pipe with a bottom opening situated within the perforated riser pipe, said vacuum extraction pipe containing groundwater prior to application of a vacuum thereto, said vacuum extraction pipe having at least one gas inlet situated below the groundwater level in the vacuum extraction pipe; while introducing a gas into the riser pipe, applying a vacuum to the vacuum extraction pipe to draw gases and liquid from the soil into the perforated riser pipe and from the riser pipe into the vacuum extraction pipe and transport both the gases and the liquid to the surface as a two-phase common stream; introducing a gas into the vacuum extraction pipe at a level below the groundwater level in the vacuum extraction pipe to initiate two-phase flow within the vacuum extraction pipe; forming from the common stream a stream which is primarily liquid and a stream which is primarily gaseous; and separately treating the separated liquid and gas streams.
Although known apparatus and processes are suitable for their intended purposes, a need remains for processes and apparatus for removing contaminants from groundwater and soil which enables contaminant removal from soils of varying air permeability and varying porosity. Further there is a need for processes and apparatus for removing contaminants from groundwater and soil which enables increased flexibility in the location of extraction wells. There is also a need for processes and apparatus for removing contaminants from groundwater and soil that can be implemented by modifying existing vacuum extraction systems.
Further, in some instances it may be desirable to remove contaminants from groundwater and soil gases from ground comprising relatively impermeable soils, such as silt, clay, mixtures of sand, silt, and clay, massive clay, or the like, or from ground comprising relatively impermeable rock, such as laminated sandstone, shale, mudstone, massive igneous and metamorphic rock, or the like. The permeability of these soils, which generally ranges from about 10.sup.-6 to about 10.sup.-8 centimeters per second or lower, is sufficiently low that many known processes for extracting ground contaminants are not suitable or efficient; known processes typically are suitable in soils with permeabilities of no less than about 10.sup.-4 centimeters per second.
Additionally, it may be desirable to remove contaminants selectively from one or more paths of preferential flow within an area of the ground, where areas of relatively low permeability are surrounded by areas of relatively high permeability. It is also desirable, in this instance, to be able to extract contaminants selectively from one or more paths of preferential flow through a single borehole or well. Extracting contaminants through a single borehole from multiple paths of preferential flow enables reduced installation costs, reduced and simpler apparatus, and less disruption to business in the contaminated area. Further, it may be desirable to apply vacuum extraction to one or more preferential flow paths while at the same time introducing a fluid (including gases and/or liquids) into one or more adjacent flow paths. In addition, it may be desirable to apply vacuum extraction to a plurality of preferential flow paths either simultaneously or in a desired sequence.